There has been know a technique in which a catalyst carrier having electric resistance is electrically energized, so that the temperature of a catalyst is raised at the time of cold start of an internal combustion engine, thereby attaining early activation of the catalyst (for example, refer to a first patent document). In addition, there has also been known a technique of determining an abnormality of a catalyst based on an output value of an oxygen concentration sensor, which is arranged at the downstream side of the catalyst (for example, refer to a second patent document). Moreover, there has also been known a technique in which when an inversion period of rich and lean states of an air fuel ratio, which is detected by an oxygen sensor arranged at the downstream side of a catalyst, has exceeded a predetermined period of time, a determination is made that the catalyst has been activated, and an amount of heat required from the time of engine starting until the activation of the catalyst is estimated, so that the deterioration of the catalyst is determined according to an integrated value of the amount of heat (for example, refer to a third patent document).
However, the temperature of an electrically heated catalyst will not go up unless it is electrically energized. For this reason, if the temperature of the electrically heated catalyst is known, it can be determined whether the electrically heated catalyst is electrically energized, so it is possible to detect a failure of the electrically heated catalyst. Here, it is considered that when determining whether the electrically heated catalyst is electrically energized, a temperature sensor is mounted on a heat generation element, for example. However, for example, SiC, which is used for the heat generation element of the electrically heated catalyst, is hard and brittle. In addition, it is hard for this material to perform thermal expansion, and hence it is difficult to embed the temperature sensor therein. Besides, it adds the cost for such processing and the cost for adding the temperature sensor. Moreover, it is also considered that the electric resistance of the heat generation element is measured and the temperature of the heat generation element is then estimated based on the electric resistance thus measured, but the relation between the temperature of the heat generation element and the electric resistance thereof may sometimes change, so it may be difficult to obtain the temperature in an accurate manner.